The concept of stress states covers those metabolic and/or behavioral reactions that are provoked in an organism as a whole by numerous exogenous aggression factors such as: inflammatory illnesses; surgery; traumatic shocks; solar, electromagnetic, or ionizing radiation; smoking; pollution; allergies; prolonged effort; emotion; cold; etc.
The type of disturbance engendered in the organism enables different types of states of stress to be distinguished, where stress can be of: chemical, microbiological, biochemical, physiological, psychic, biophysical, or pharmacological order.
It is well established that under the effect of some of the above-mentioned factors, the organism produces oxidizing agents that generate a kind of stress referred to as oxidation stress. These agents are in the form of reactive oxygen species (ROS). For example, in the event of prolonged effort, demand for oxygen increases, and consequently oxygen consumption increases, thereby leading both to a state of hypoxia and to overproduction of ROS agents.
The production of ROS agents is then associated with normal endogenous biochemical mechanisms. In particular, in the respiratory system, 2% to 4% of the oxygen involved is reduced incompletely giving rise to ROS agents.
ROS agents are free radicals, atoms, or molecules that are unstable and reactive, usually presenting one or more lone electrons. The main ROS agents are: singlet oxygen (O—), superoxide anion, hydrogen peroxide, hydroxyl radical, nitrogen monoxide, or hydroperoxy radicals (produced during peroxidation of membrane lipids, particularly those constituted by polyunsaturated fatty acids).
Biologically speaking, oxidation stress leads to:
lipid peroxidation targeted on cell membranes and mitochondrial; polyunsaturated fatty acids (PUFA) are attached and released ethane (ω-3 PUFA) and pentane (ω-6 PUFA);
protein oxidation of mitochondrial proteins, leading to malfunction of the respiratory system and to a reduction in the amount of energy produced by cells; or
oxidation of mitochondrial DNA (mtDNA) which leads to mutations that also lead to malfunction of the mitochondria.
Oxidation is the main cause of cellular aging and of diseases due to age (cancers, cardiovascular disorders, reduced immune functions, brain malfunction such as Alzheimer's disease, or cataracts). This is corroborated by the fact that anti-oxidant foodstuffs (ascorbic acid, tocopherol, and carotenoids of fruit and vegetables) contribute to combatting the appearance of such degenerative diseases.
Ethane and pentane constitute known biomarkers for oxidation stress states. As mentioned above, oxidation stress gives rise to metabolic disorders including lipid peroxidation which leads to the formation of ethane and pentane. These products are volatile substances which are subsequently eliminated in breathed-out air.
Pentane appears to be more significant than ethane in vivo since, in membranes, lipids of ω-6 PUFA structure predominate over those of ω-3 PUFA structure. The measured ethane/pentane concentration in breathed-out air is proportional to the oxidation stress state.
Nevertheless, it is important to have a quantitative marker for stress states, and in particular for oxidation stress.